M Stands for More: Not to mention, with M-class tuners, madness.

The Lorinser's stock 4.3-liter V-8 was fitted with a Vortec supercharger that employs a trick electromagnetic decoupling clutch to reduce scavenging power losses at low rpm. Between the blower and the Lorinser "Dual Twin" exhaust system, output was raised from 268 to a heartening 349 hp, says Lorinser. Alas, the kit failed to translate into big speed: The Lorinser rumbled to 60 mph in 7.5 seconds and turned in a 15.9-second quarter-mile, second slowest of the bunch.

A shame, really, because the Lorinser offered the most handsome body-cladding kit and beautiful star-patterned alloy wheels. Its braking measurement was also the best of the clan, its four-pot Brembos stopping from 70 mph in 168 feet, 10 feet shorter than the AMG.

RENNTech ML60RSMaybe AMG and Lorinser should steal a page from RENNTech and completely reengineer the suspension. Hartmut Feyhl's Florida firm dropped the ML60RS a full three inches, added dual-adjustable Koni coil-over shocks, and then shod it with two-piece O-Z Futura lace wheels (9.5 by 20 inches) wrapped with BFGoodrich Comp T/A 295/40ZR-20 tires. Skinned of its roof rack, the lower-than-low ML60RS looks like a Hovercraft.

But, Feyhl explained, because there is so much droop built into the SUV's suspension geometry, once you lower it more than a couple of inches, it's necessary to relocate the upper-control-arm pickup points, which he has done (kids, don't try this at home).

The result feels less sport-ute than sports car -- a Ferrari SUV. "The driving feel approaches perfection," noted one of many rhapsodic log entries. "Very subtle shock tuning. Almost creamy over smooth roads yet muscular control of body motions when needed."

Out on the open range, in vast sweepers at supernumerary speeds, the ML60RS tracks like a bobsled with nary a niggle of body roll. Even with 20-inch BFGs, the RENNTech's steering was linear and precise, preserving the oily smoothness of the stock rack-and-pinion. The ML60RS spanked the lane-change test, tripping the lights at 58.6 mph (second fastest was the Lorinser at 57.2 mph) and registering a prodigious 0.86 g on the skidpad.

Yet for all its dynamic prowess, the ML60RS's stock in trade is horsepower, great whacking gobs of it, for which RENNTech charges great whacking gobs of money: $49,900 just for the engine upgrades.

RENNTech begins with a Mercedes 5.0-liter block with a 97-millimeter bore and reams it out to 100mm, preserving the low-friction silicon-aluminum surface using a special proprietary process. Then it adds a billet-steel crank with colossal titanium con rods, bringing the stroke up to just under 95mm for a total displacement of 5954cc.

The tally is 408 naturally aspirated horsepower at 5800 rpm and 464 pound-feet of torque leveled off between 2400 and 5000 rpm, enough to launch the 4562-pounder to 60 mph in a crackling 5.2 seconds. RENNTech exploits the fact that in these Merc three-valvers torque doesn't peak so much as plateau right across the rpm range. We were suitably dumbfounded by the top-gear 30-to-50-mph time of 2.8 seconds. "Huge power is everywhere, anytime," a test driver wrote.

"When the engine lights, you know you are in the presence of greatness," wrote another test driver of the RENNTech's distinctive, throaty growl.

In the interest of balance, the RENNTech's brakes are likewise colossal: 15-inch front and 14-inch rear discs answering to Brembo four-piston calipers.

Complaints? We had a few. The FAB aero kit the RENNTech wears is a little sophomoric. And then there is the price, which will buckle your knees like a shot of poisoned tequila: $136,991.

Stillen GTM 430 S/CAlthough Steve Millen's M-class tuning operation is still in its infancy, the company portfolio has packages for Yukons, Suburbans, Expeditions, and other Detroit iron. Stillen has therefore developed a style.

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